A heavy-duty circuit-breaker is known from the prior art, which has a contact tulip as the arcing contact piece, which forms a flat contact with a current-carrying element in order to carry a short-circuit current. A tube composed of erosion-resistant material is provided within the contact tulip and extending into the current-carrying element, and is intended to protect the interior of the contact tulip against hot gas, with the gas being heated by an arc which is based on the arcing contact piece, and with the gas flowing through the contact tulip to beyond the current-carrying element.
Unless adequate protection is provided, a hot-gas flow such as this can remove material from the current-carrying element and/or from the contact tulip, as a result of which this can lead to degradation of the electrical contact between the contact tulip and the current-carrying element. This can result in increasing  contact resistance, and even in failure of the contact.
The tube composed of erosion-resistant material is screwed into the current-carrying element and, in the part in which it is arranged within the contact tulip, has an external diameter which is larger than the internal diameter of the contact tulip at that respective point.
The provision of a tube such as this composed of erosion-resistant material considerably reduces the cross-sectional area available for the gas to flow through. If this cross-sectional area is intended to remain approximately constant, in order to maintain similar outlet-flow speeds, a larger contact tulip and a larger current-carrying element must be provided (for the same cross sections available for the short-circuit current), thus resulting in a heavy-duty circuit-breaker that is larger overall.
EP 0 642 145 A discloses a circuit breaker having male contact pin and contact tulip, in which the contact fingers of the tulip have an axial cutout in order to hold a tube therein, which is used as a radial-movement limiter for the contact fingers. A further protective tube, for protection against hot gas, is provided in the interior of the contact tulip, for thermal protection against erosion.
EP 0 290 950 A discloses a gas-blast circuit breaker which has contact fingers in the form of tulips as an arcing contact piece, which contact fingers, together with a cylindrical erosion contact, form the arcing contacts. A tubular body which can be moved axially is guided within the contact tulip and is pushed by a spring in the direction of the erosion contact during a disconnection process.
Furthermore, EP 0 932 172 A2 discloses a circuit breaker having a tulip contact piece, whose sprung arcing contacts and the tubular piece arranged thereon are protected against erosion by an arc-resistant insert. The flow cross section in the tulip contact piece is disadvantageously reduced because the insert rests internally on the arcing contacts and on the tubular piece.
It is therefore desirable to provide a heavy-duty circuit-breaker which is as compact as possible but nevertheless offers protection against the hot-gas-induced contact degradation that has been mentioned.